Attributes
Here, each attribute is described in detail, including weak points that one has to be careful about.
image
The image attribute is used to upload a file (much like the file attribute), however the image attributes takes as a parameter, the file extension of an image format. And whenever the image is set the supplied filename is converted to a picture of the given type.
ImageMagick convert quirks
All the image attributes of this module, uses the ImageMagick convert command to convert/scale/thumbnail the images.
The current ImageMagick in stable Debian (woody), does not support the -thumbnail command, so this module just uses -scale instead at the moment.
There is still reason to use the thumbnail attribute though, as you won't have to change your code when the new Debian is relased (which is hopefully soon).
scale and thumbnail
scale and thumbnail provides one additional image to the main image (that has the same size as the uploaded image).
scale and thumbnail takes as a parameter, the size of the scaled or "thumbnailed" image, this size is defined in the manner of width x height, e.g.: 640x480
Scale does a "hard" scale, the aspect ratio of the image is not maintained.
Thumbnail does a "soft" scale, the aspect ratio is maintained but the height/width of the image is maximum that of the supplied parameter value.